Understanding the molecular and cellular basis of neuropsychiatric disorders is one of the biggest and most significant challenges for the 21st century in neuroscience. Attention deficit hyperactivity disorder (ADHD) is the most common childhood psychiatric disorder and is characterized by inattention, distractibility, impulsivity, and/or the presence of hyperactivity. Numerous laboratories have shown that ADHD is highly heritable (approximate heritability is 0.8) although environmental factors also importantly influence its pathogenesis. To further advance our understanding of ADHD's molecular pathogenesis it is desirable to establish multipotent stem cells with the genetic backgrounds of ADHD and healthy subjects for biological and molecular comparisons. In 2006, Shinya Yamanaka and his colleagues published their groundbreaking work showing that pluripotent stem cells, so called "induced pluripotent stem (iPS) cells, can be generated from somatic cells by retroviral transduction of four transcription factors (i.e., Oct4, Sox2, Klf4 and c-Myc). Strikingly, several groups, including Yamamaka's, soon demonstrated that human iPS cells could be generated by similar methods. Although this iPS technology is still at an early stage and needs further development, based on these pioneering studies and our own preliminary results, we hypothesize that potential pathogenic mechanisms of ADHD can be investigated by generating ADHD-specific iPS cells and by using in vitro differentiation studies, comparing them with those of iPS cells derived from healthy subjects. Toward this long-term goal, during the R21 phase of the project, we propose (1) to establish multiple iPS lines from healthy and ADHD subjects, (2) to validate iPS cell lines by cellular, molecular, and differentiation analyses, and (3) to address whether the RAG1/RAG2 VDJ recombinase system can be used to screen and/or monitor human iPS cells'identity. In addition, during the R33 phase, we propose (1) to characterize the differentiation of individual iPS cell lines to expandable neural progenitors/precursors, (2) to characterize their differentiation to relevant neuronal subtypes such as dopaminergic and noradrenergic neurons, and (3) to compare cellular and differentiation properties of iPS cell lines from healthy and ADHD subjects for potential pathogenic mechanisms. PUBLIC HEALTH RELEVANCE: Recent groundbreaking work by Shinya Yamanaka and his colleagues introduced the "induced pluripotent stem (iPS) cell" technology, a tantalizing new method generating genetically matched pluripotent stem cells without embryo destruction. To fully utilize this revolutionary technique, we propose to further advance this method by establishing a human iPS screening/monitoring system, and to generate and characterize multiple iPS lines from healthy and ADHD subjects. This approach will advance the iPS cell technology and provide a platform for investigating the biological and molecular mechanisms underlying ADHD pathogenesis.